EP 0 436 906 B1, which is incorporated by reference, discloses a combined brake caliper of generic type for a motor vehicle disk brake having an axial bearing. The brake caliper comprises a housing having a bore hole, in which a brake actuating piston is displaceably arranged. For parking brake operations, a shaft is rotatably supported in the brake housing, the shaft passing through the brake housing and being connected to one ramp element of a ramp arrangement. A second associated ramp element is arranged, fixed to the housing. Owing to a wedge mechanism-like action between the shaft and the ramp arrangement, the shaft under a rotational actuating movement also experiences an axial displacement. The shaft transmits this axial displacement to a spindle of an adjusting device, an axial bearing being provided between the shaft and the spindle. The axial displacement is transmitted to the piston via the adjusting device. Here a casing of the adjusting device is rotationally fixed to the ramp arrangement integral with the housing.
In order to relieve the components of the torsional safeguard, it is proposed to produce the axial bearing from sheet steel, which is provided with a low-friction coating of polytetrafluoroethylene, in which a lead-copper mixture is embedded.
It has emerged that, under particularly intensive stresses and/or over a long operating time, steel sheets coated in this way may suffer from the drawback that the coating peels off. This peeling occurs particularly when some, perhaps slight, skewing prevails between the friction pairing involved. Then an excessive surface pressure due to localized over-stressing of the coating causes it to peel off in the area of a boundary surface between the base material and the coating material of the axial bearing. As a result the friction-reducing characteristics of the axial bearing are lost, and there is the risk that peeled coating parts or particles might get into the brake fluid and contaminate the latter. It should be noted that axial alignment errors or skewing cannot be entirely excluded in the brake calipers of generic type, for which reason a convexly curved axial bearing is particularly recommended in EP 436 906 B1, in order to avoid these problems.